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Triggered spark gap vs rotary spark gap

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ifryd

Wed Dec 28 2011, 11:50AM

Registered Member #4215 Joined: Wed Nov 16 2011, 09:45PM
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Posts: 32

Hello

As in the subject. What device would be better for switching high currents with high frequency up to 1000Hz?
What type of material use for electrodes?

Steve Conner

Wed Dec 28 2011, 12:25PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The rotary can dissipate heat better because of the airflow generated by rotation. But DIY triggered gaps are often built with an air blast from a vacuum cleaner motor, which solves the heat problem.

Copper, brass and tungsten are good electrode materials. One popular triggered gap for Tesla coils used hollow brass electrodes (some sort of plumbing fitting slightly modified) with the air blast passing through them.

A triggered gap offers agile control of the break rate. You can trigger it any time with an electronic pulse to an ignition coil. A rotary gap is stable, but it runs at the speed it runs at.

ifryd

Wed Dec 28 2011, 06:03PM

Registered Member #4215 Joined: Wed Nov 16 2011, 09:45PM
Location:
Posts: 32

What do you think about this triggered spark gap:

I want to do something simillar. I have controlling circuit with ignition coils but:

I want to use ordinary screws as in youtube movie and also I would like to enclosure it to reduce ozone in air and uv radiation.

Each time when I try to enclosure spark gap I find it stops working after time but is it caused by bad electrodes or by the same air which becomes electrified. (I see yellow fumes after time) How to solve this problem with ozone? I want to make it safe for operating...

Pinky's Brain

Wed Dec 28 2011, 06:07PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

The rotary spark gap makes some things easier, with a triggered spark gap you probably need a pulsed charging circuit (easiest way to extinguish the arc). BTW, what kind of hold off voltage, currents and switching speeds are you looking at? Thyristors are cheap ...

Steve Conner

Wed Dec 28 2011, 06:28PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The yellow fumes are oxides of nitrogen, some rather toxic gases.

A high power spark gap won't work when sealed in a box. It needs an air blast to keep the electrodes cool and remove ions for good quenching. It should also dilute the ozone and NOx, and stop them from building up to dangerous concentrations, unless you then use it in a tiny sealed room.

But most machines that use high power spark gaps are not things you'd want to be locked in a room with anyway.

Those bolts are steel, usable but not the best material for high power operation.

ifryd

Wed Dec 28 2011, 07:22PM

Registered Member #4215 Joined: Wed Nov 16 2011, 09:45PM
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Posts: 32

Thank you friends for fast answers...
Maybe I will answer differently. I want to make Tesla coil which would discharge primary with desired frequency (from 250 up to 1000Hz) also it has to be safe to operate in room. I don`t think thyristor would be appropriate to my design as I want to obtain rapid discharge of the capacitors.

What about triggered spark gap in oil? (are there the same problems : oil saturation etc?) I don`t have any experience with these gaps. What voltages break down 1mm of mineral oil? I also want to mention that I have circuit with ignitions coils to make discharging sparks up to 3cmeters.

What I have: 15kV power supply from Obits, circuit controller with ignition coils for making ignition sparks, 2 x 16kV capacitors and tesla coil...

Pinky's Brain

Wed Dec 28 2011, 09:18PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Oil would decompose ... in fact almost any liquid you could use would decompose ... unless you want to use liquid sulphur.

Steve Conner

Wed Dec 28 2011, 09:47PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Also a good Tesla coil will produce lots of ozone and NOx from the main high voltage discharge, even if you stopped the spark gap from making any. So, no point in worrying too much.

You could always put the whole apparatus in an aquarium tank full of argon.

Platinum

Wed Dec 28 2011, 10:03PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

I made a spark gap from a hair drier.

Alex M

Wed Dec 28 2011, 11:33PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Platinum wrote ...

I made a spark gap from a hair drier.

Could you explain some moar?

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